Title Prahaar Summary 2025_Geography and DM_E-Book.pdf ✅

Geography and Disaster Management 3 GEOGRAPHY AND DISASTER MANAGEMENT 1. GEOMORPHOLOGY Origin and Evolution of Earth Ê Nebular Hypothesis: Kant and Laplace proposed a hot gaseous nebula that cooled and contracted, forming rings that condensed into planets. Fails to explain angular momentum difference between sun and planets. Ê Planetesimal Hypothesis: Chamberlain and Moulton suggested a passing star pulled material from the sun to form planets, but intense early heat challenges gas condensation. Ê Tidal Hypothesis: Jeans and Jeffrey proposed tidal forces from another star formed planets, but it ignores the sun’s internal disruptions. Ê Protoplanet Hypothesis: Rotating nebular vortexes attract material to form protoplanets and satellites. Ê Big Bang Theory: Georges Lemaître theory with evidence provided by Hubble. Hubble’s theory suggests the universe began 13.6 billion years ago with a massive explosion. Age of the Earth- Ê Estimated age: 4.54 billion years (±50 million). Determined via radiometric dating using decay of short- lived (C-14) and long-lived (K-14 → Ar-40) isotopes. Motions of the Earth- Rotation: Ê Spinning on the axis creates day-night cycle, bulging at equator, sunrise/sunset, Coriolis effect, and apparent celestial motion. Ê Revolution: Elliptical orbit around Sun; speed varies (fastest at perihelion). Effects of Earth’s Revolution- Ê Seasonal Changes: Axis tilt causes varying sunlight. Ê Daylight Length: Longer days in summer, shorter in winter. Ê Wind Belts: Revolution shifts global wind patterns. Internal Structure of the Earth- Ê Divided into Crust, Mantle, and Core (based on seismic studies). Ê Crust: Oceanic (5–10 km) and continental (35–70 km). Key layers—Sial (silica-aluminum) and Sima (silica- magnesium). Ê Mantle: 84% of Earth’s volume, from Mohorovicic discontinuity to 2,900 km depth; upper and lower mantle separated by velocity zones. Ê Core: Liquid outer and solid inner core (nickel-iron), ~6,000°C, >3 million atmospheres pressure. Inner core slowdown may slightly alter day length. The Three North Poles- Ê Geographic Pole: Axis point on Earth’s surface. Ê Magnetic Pole: Northern point of magnetic field, drifts due to outer core changes. Geomagnetic Pole: Magnetosphere’s northern tip; shifting pole affects navigation and GPS updates. Earth’s Magnetosphere- Ê Earth’s interior acts as a giant magnet, forming a magnetosphere that shields against solar wind and harmful radiation. Molten iron in the outer core generates the magnetic field extending far into space. Formation of Auroras (UPSC 2024)- Ê Solar wind particles interact with the magnetosphere near poles, creating aurora borealis (north) and aurora australis (south). Collisions with atmospheric atoms release light—green/red (oxygen) and blue/purple (nitrogen). Geomagnetic Storm- Ê A G5 solar storm caused severe magnetospheric disturbances from coronal mass ejections (CMEs). Impacts: GPS disruptions, power grid failures, radiation hazards, and pipeline corrosion. Distribution of Oceans and Continents- Ê Continental Drift Theory (UPSC 2013)- Alfred Wegner (1912): Continents were once united as Pangaea surrounded by Panthalassa. Evidence: Jigsaw fit (Africa–S. America), identical rocks, glacial tillite, gold placer deposits, and Mesosaurus fossils. Forces: Polar fleeing force (Earth’s rotation) and tidal force (Sun/Moon). Forces now rejected. Ê Convectional Currents Theory (1930s, Arthur Holmes)- Mantle convection, driven by heat from radioactive decay, causes slow continental drift. Ê Seafloor Spreading Theory (1961, Harry Hess)- New ocean floor forms at mid-ocean ridges and moves outward; subducts at trenches. Ê Plate Tectonics Theory (1967, McKenzie, Parker & Morgan)- Lithosphere divided into plates (continental/oceanic) moving horizontally a few cm/year. Ê Mantle Plume- Hot upwelling magma columns (e.g., Hawaiian Islands, Deccan Traps) explain intraplate volcanism and continental flood basalts. Plate Boundaries- Tectonic plates move due to mantle convection, forming three types of boundaries: Ê Divergent Boundaries: Plates move apart at mid-ocean ridges, forming rift valleys and basalt/gabbro rocks.